As a hydraulic ramming apparatus, various types of ramming apparatus (devices) are well known.
For example, a hydraulic ramming apparatus disclosed in Japanese Utility Model Publication No. Hei 6-21923 is well known. In this hydraulic ramming apparatus, a piston is slidably inserted into a cylinder bore formed in an apparatus (device) body so as to enable the piston to vertically move within the cylinder bore, and to thereby define an upper pressure chamber and a lower pressure chamber. In addition, the piston is protruded downwardly from the device body, and a ramming plate is attached to the protruded end portion thereof. Further, a change-over valve for switching circuits of pressurized oil is provided in the device body.
In the hydraulic ramming apparatus, when the change-over valve is switched by the vertical movement of the piston and the pressurized oil is alternately supplied to or discharged from the upper pressure chamber and the lower pressure chamber to vertically move the piston, the ramming plate is vertically moved to thereby ram or compact the ground.
However, in the hydraulic ramming apparatus thus constructed, since the ramming plate is attached to the protruded end portion of the piston which is vertically movable by the hydraulic pressure, the ramming apparatus is applied to only the ramming or compacting work and the apparatus is not available, for example, for crushing work using a chisel.
That is, in a case where rocks or the like are crushed by utilizing the chisel, when the chisel in a state of being abutted against rocks or the like is hammered by the vertical movement of the piston and impact points on the rock by the chisel is converged to one point, the rocks or the like can be efficiently crushed.
However, as described above, when the chisel is attached to the protruded end portion of the piston, the chisel is liable to vertically move together with the piston, and the impact points of the chisel against the rock are apart from each other in every hammering operation and thus the impact points cannot be converged, so that it is difficult to efficiently crush the rocks.
In addition, in the hydraulic ramming apparatus described above, there may be posed a problem that a lateral force is liable to be applied onto a sliding portion of the piston and the lateral force will damage the sliding portion of the piston, which may result in oil leakage.
Namely, when the ground is subjected to the ramming operation by using the vertically moving ramming plate, the lateral force other than upward reactive force is also applied to the ramming plate due to irregularities of the ground. The lateral force is transmitted to the piston, and the piston is obliged to vertically slide within the cylinder bore while the piston is obliquely impressed to the cylinder bore formed in the device body, so that there may be a case where the sliding portion of the piston is damaged. When the sliding portion of the piston is damaged, there may cause a problem that the pressurized oil charged in the upper and lower pressure chambers leaks, thus resulting deteriorated reliability of the device.
In addition, the piston of the above-mentioned hydraulic ramming apparatus comprises the sliding portion and the protruded end portion, so that an entire length of the piston will become large and it requires significant amounts of time to work and assemble the piston system.
That is, the sliding portion of the piston is required to be subjected to a precision work and a heat-treating work so as to prevent the pressurized oil from leaking therefrom. However, since the entire length of the piston sliding portion long, an initial set-up for the work becomes complicated and will disadvantageously prolong the working time of the piston assembly.
Furthermore, a dimensional tolerance between the piston sliding portion and the cylinder bore is extremely small and both the piston and the cylinder bore are strictly required to be aligned in a straight line and the piston is required to be inserted into the cylinder bore with a high degree of accuracy. However, the entire length of the piston becomes long due to existence of the protruded end portion as described above, so that the inserting operation cannot be performed easily which prolongs the assembling time for the device.
Therefore, the present invention is achieved for solving the aforementioned problems and an object of the present invention is to provide a hydraulic ramming apparatus which and is also applicable to a crushing operation using a chisel or the like, and is substantially free from the oil leakage and enables the working time to be shortened and the assembling time.